A Time Division Multiple Access, TDMA, radio communication system divides the time space in time slots on a particular transmitting frequency. The time slots are grouped together in TDMA-frames and each user gets one time slot. This means that there are as many users as there are time slots in each frame and sharing the same radio frequency. That is the case at least in principle, but some time slots or channels are normally reserved for control information.
When a time slot is assigned to a user in the way described the connection is regarded as circuit switched and the user owns the time slot as long as he needs the connection. Circuit switched connections are suitable for connections where there is a continuously ongoing flow of information over the channel, like voice communication, which is also sensitive to delay. On the other hand when the traffic is data which has a bursty character and which is not that delay sensitive, the user does not need the channel all the time. He only needs it when there actually is a data packet to send or receive. In the mean time the channel could be used by others. This is the background to packet switched connections where several users may share the same channel.
The universal TDMA-system GSM was originally designed for circuit switched connections but by adding some extra nodes, this existing system may also be used for packet switched connections, the GPRS-solution (General Packet Radio System).
In packet switched solutions, each user gets one or several time slots reserved for his disposal. Other users may, however, use the same time slots and there is a need for scheduling the time slots on the different users, especially when they request service at the same time. Depending of type of data, and need for speed requested among the users, different classes of Quality of Service, QoS, are defined. The QoS for a certain data packet also has an impact on the scheduling and users with high class QoS will be favoured in relation to those having lower classes. Thus depending on several parameters the scheduling could become quite complicated.
Current available scheduling methods for GPRS are “Weighted Round Robin” and “Virtual Clock Multiplexing”. Reference could also be made to the following literature:                WO 2001/525 88 assigned to Quallcomm Inc. publ Jul. 19, 2001.        Resource Allocation in GPRS Wireless Network, Tripathi et al, Personal Wireless Communications, 2000 IEEE International Conference, 2000, p. 388-394.        Scheduling and QoS in GPRS, Sau et al, Universal Personal Communications 1998, Vol 2 p. 1067-1071.        An Air Interface Solution for Multi-rate General Packet Radio Service, Taaghol et al Vehicular Technology Conference 1997, vol. 2, p. 1263-1267.        